The present invention relates generally to photographic printers and more particularly to a photographic printer which provides apparatus for measuring the scanned and large area transmissive densities of negatives, and the large area reflective density of reflective test patches.
In the process of developing photographic negatives, printing the negatives, and developing the prints, it is necessary to measure various density characteristics of both negatives and prints. For example, to monitor the quality of a film processor, it is necessary to measure the transmissive characteristics of a developed strip of transmissive test patches, commonly referred to as a film process control strip. To properly control exposure when printing negatives, it is common practice to scan the transmissive characteristics of each negative at a plurality of discrete locations whereby to measure the scanned transmissive density of each negative. When printing certain types of negatives it may also be desirable to measure the large area transmissive density (LATD) of these negatives, in lieu of or in addition to the measurement of the scanned transmissive densities. To monitor the quality of a film processor, it is necessary to measure the LATD of transmissive test patches developed in the film processor. To monitor the quality of a paper processor, it is necessary to measure the reflective density of a developed strip of reflective patches, commonly referred to as a paper process control strip. To monitor the quality of a printer, it is necessary to measure the reflective density of a printer control test print, exposed in the printer and processed in the paper processor. These measurements are used to control the printing process.
To perform these various densitometric measurements, photographic laboratories often must have available several pieces of sophisticated equipment, including transmissive and reflective densitometers. High costs are associated with purchasing and maintaining this equipment.
Some printers include apparatus for performing one or two of the above-described densitometry measurements. U.S. Pat. No. 4,526,462 to Hope et al. shows a color printer incorporating red, green, and blue photocells connected to amplifiers for measuring the transmissive density of negatives, and a probe for measuring the reflective density of a test print. Both the reflective and transmissive densities are input to a microprocessor, which subsequently calculates exposure times for negatives. Hope et al. makes no provisions for measuring scanned transmissive densities of negatives. Further, the printer in Hope et al. requires the use of four separate light sensors to measure the various densities: one in the probe for measuring reflective densities, and three disposed at an apparent right-angle to the optical path for measuring the transmissive densities. Hope et al. suffers the disadvantages inherent in maintaining and calibrating this number of light sensors.
U.S. Pat. No. 3,083,614 to Veit shows a photographic printer wherein a single photocell is pivoted between a first position where it is used to measure the transmissive density of a negative, and a second position wherein it is used to measure the reflective density of paper. Veit, however, does not provide for measuring the scanned density of the negative. Further, the time required to pivot the photocell of Veit limits the speed at which the printer can be operated.
U.S. Pat. No. 3,462,221 to Tajima et al. shows a photographic printer wherein a first photocell is employed at a first location to measure the transmissive density of a negative, and a second photocell is employed at a second location to measure the reflective density of developed prints. Measurements made by these first and second photocells are used to control both the printing and developing processes. Tajima et al. suffers from the disadvantages inherent in maintaining and calibrating two separate photocells. Further, Tajima et al. does not provide for measuring the scanned transmissive density of a negative.
It would thus be desirable to provide a photographic printer which, with the inclusion of as few additional components as possible, provides the capability to measure the scanned and large area transmissive density of negatives (or transmissive test patches), as well as the reflective density of prints (or reflective test patches). It would be further desirable if such a photographic printer were capable of operating at relatively higher speeds than hand-operated printers of the type shown in Veit above.